Conventionally, there is a known motor in which a dynamic pressure gas bearing supporting a shaft by a sleeve is used. Such a motor is disclosed in Japanese Unexamined Utility Model Application Publication No. 03-101154.
However, the above conventional motor has a structure in which simply by rotating the shaft, a dynamic pressure is generated between an outer circumferential surface of the shaft and an inner circumferential surface of the sleeve, so that bearing rigidity is provided. Thus, when, due to an external disturbance or the like added to the motor, the shaft and the sleeve swing relatively in the direction in which the rotation axis of a rotating body is inclined and are brought into contact with each other, a contact friction torque of the dynamic pressure gas bearing is increased, and seizure is generated by adhesion or galling of the dynamic pressure gas bearing. Thus, fatal damage could possibly be made to the dynamic pressure gas bearing.
Therefore, in order to sustain the rotation safely, there is another known motor including a sliding bearing, a rolling bearing provided on the outer side of this sliding bearing, and a rotation regulating means that regulates rotation of the rolling bearing until a rotation torque transmitted from the sliding bearing to the rolling bearing becomes or exceeds a reference rotation torque. This motor is described in Japanese Examined Utility Model Application Publication No. 57-1132.
However, the above conventional rotation regulating means has a contact structure in which an elastic member and a coupling member, which are attached to an outer annular member, are abutted with an inner annular member. Thus, there is a problem that even when the transmitted rotation torque exceeds the reference rotation torque but the rotation is made by the rolling bearing, the elastic member is abutted at each rotation and the elastic member is damaged, or a problem that when the transmitted rotation torque exceeds the reference rotation torque, the coupling member is broken and the structure itself of the rotation regulating means is damaged.